Slow crank when hot

[Alpine85]

Okay so I bought my 81 notch about six months ago and I've been doing some work to get it in road worthy condition again. One of the things I did was relocate the battery to the trunk and ever since this it has had a really slow crank when it gets hot. The kit I bought came with 2 gauge power wire, four gauge ground wire and I ran a 2 gauge ground wire from the block to the frame rail after I took a flapper wheel to it. The ground wire off the battery goes through the trunk floor and attaches to the frame rail that had the same flapper wheel treatment. I do realize that the wire I have is on the small size but I feel the symptoms I'm getting indicate he soak. It also has a brand new starter that I put in at the same time that I relocated the battery. The car does have BBK long tube headers with factory style starter so it is a close fit and I'm sure it gets hot. I was planning on doing a voltage drop test this weekend but I'm uncertain what an acceptable reading would be.

So my question is what would the acceptable volt drop be, what is the best way to cure heat soak, do I need larger battery cables?

thank you for your time and advice.

[Walking-Tall]

Starting problem began after battery relocation. That's a sign. 1-gauge (for all + and - cables) is good, 0-gauge is better, for least resistance. I suppose it's possible and coincidental, but IHMO a "heat soak" problem would have been a problem prior to relocating the battery. Has this got a traditional, non-solenoid equipped Ford starter on it? Non-solenoid equipped Ford starters don't get affected like that, or have the closer proximity to headers, or the tight tolerances that are within the solenoid on such equipped starters, like GM or high-torque starters, which do get affected by heat like you're describing. Ford starters would have to be incredibly heated before they will "heat soak" and close up their comparatively generous internal clearances, jamming them up, slowing down or halting starter rotation.

The lesser the drop, the better, period. IMHO, heavier cables would make this problem go away. Good luck with it

[homer302]

They start 700HP Hellcats when they are hot with cables much smaller what you already have. I am wondering about the integrity of the ENDS installed on the cables or perhaps even the quality of the wire itself. That being said, I had this same problem on a 1984 GT I had and it was pretty much cured (much improved at least) by installing a higher quality, larger gauge battery cable and end so who knows? Maybe it was the larger gauge that fixed it. I have seen hundreds of far higher HP cars started with standard size small cables though.

[Alpine85]

Thank you for your help. It sounds like I'll be putting new larger cables on it tomorrow. To answer your question walking tall my solenoid is mounted inside the passenger side fender. I thought the heat would add resistance to the winding in the starter motor and that's what caused heat soak. Why does the heat have an effect on the solenoid? Isn't it just a simple contact?

[Walking-Tall]

Good, up on the fender well is where a starter solenoid belongs, IMHO. Heat from headers etc can have an affect on the starter-mounted solenoids simply because they're right close to the potential exhaust heat, and because they've got a number of jobs to do. As well as contact control, they are much more of an intricate and mechanical component to the physical kicking out of the starter's gear, enclosed in thin sheet metal with tighter clearances inside of a cylinder-inside-a-cylinder type of scenario.



... as opposed to the fairly loose clearances around the plate, that is a simple contact, inside a traditional fender-mounted Ford solenoid. The Ford fender-mounted solenoids are a simple set of contacts, a heavy duty relay of sorts with one job. BTW, with your car being an '81, hopefully it's got the old style solenoid. I have repeatedly found that the older, vertical-acting Ford solenoids function reliably better, with only straight up and down movement of the contact plate inside, and last longer than the newer horizontal-acting ones, because there's no side loading and cocking of that contact plate inside the older ones.

[dynodon64]

Drop the ground cables to the frame and run a new ground cable from the battery all the way up to the stock location on the block. I use welding cable,it's a lot more flexible and easier to run. Ground cables to the frame will always give you problems. It gets even worse with fuel injected cars.